1. Field of the Invention
The present invention relates to the field of hydraulic pumps and supplies, including but not necessarily limited to those for operating engine Hydraulic Valve Actuation (HVA) and Hydraulically Intensified High Pressure Fuel Injection (HPFI) systems.
2. Prior Art
Hydraulically actuated fuel injectors are well known in the prior art, and hydraulic engine valve actuation is also known in the prior art. Both of these systems take significant power for their operation, so that overall engine efficiency is significantly affected by their operation. In the case of fuel injectors, power for high pressure fuel injection is required for good fuel atomization, and in the case of hydraulic engine valve actuation, the power requirement is generally more than offset by improved engine efficiency and flexibility in operation. However, engine efficiency can still be substantially improved by reducing engine output requirements for providing the needed hydraulic power.
In the prior art, various forms of fixed displacement pumps and variable displacement pumps have been used. Typically fixed displacement pumps have been oversized for many operating points and pump energy is wasted. Variable displacement pumps may not be able to supply multiple hydraulic rails. In general, prior art pumps are not able to capture and store energy during engine braking, or to supply power to engine.
Positive displacement pumps are also known in the prior art that include valving that allows coupling excess pump capacity back to the input of the pump to allow continuous operation of the pump, but with the excess pump capacity being pumped through a very low pressure differential. Such a system is disclosed in U.S. Pat. No. 7,185,634 entitled “High Efficiency, High Pressure Fixed Displacement Pump Systems and Methods”, owned by the assignee of the present invention.